U.S. patent number 11,186,706 [Application Number 16/097,319] was granted by the patent office on 2021-11-30 for machine direction oriented films comprising multimodal copolymer of ethylene and at least two alpha-olefin comonomers.
This patent grant is currently assigned to Borealis AG. The grantee listed for this patent is Borealis AG. Invention is credited to Paulo Cavacas, Audrey Gensous, Anh Tuan Tran.
United States Patent |
11,186,706 |
Tran , et al. |
November 30, 2021 |
Machine direction oriented films comprising multimodal copolymer of
ethylene and at least two alpha-olefin comonomers
Abstract
A machine direction oriented film comprising a multimodal
copolymer of ethylene and at least two alpha-olefin-comonomers
having: a) a density of from 906 to 925 kg/m.sup.3 determined
according to ISO 1183, b) an MFR.sub.21 of 10-200 g/10 min
determined according to ISO1133, wherein the multimodal copolymer
of ethylene comprises c) a first copolymer of ethylene and a first
alpha-olefin comonomer having 4 to 10 carbon atoms; and d) a second
copolymer of ethylene having an alpha-olefin comonomer different
from the first copolymer, said second alpha-olefin comonomer having
6 to 10 carbon atoms.
Inventors: |
Tran; Anh Tuan (Linz,
AT), Cavacas; Paulo (Coutada, PT), Gensous;
Audrey (Dax, FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Borealis AG |
Vienna |
N/A |
AT |
|
|
Assignee: |
Borealis AG (Vienna,
AT)
|
Family
ID: |
1000005966688 |
Appl.
No.: |
16/097,319 |
Filed: |
April 28, 2017 |
PCT
Filed: |
April 28, 2017 |
PCT No.: |
PCT/EP2017/060285 |
371(c)(1),(2),(4) Date: |
October 29, 2018 |
PCT
Pub. No.: |
WO2017/186953 |
PCT
Pub. Date: |
November 02, 2017 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20200325316 A1 |
Oct 15, 2020 |
|
Foreign Application Priority Data
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|
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Apr 29, 2016 [EP] |
|
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16167801 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08L
23/0815 (20130101); B29C 48/10 (20190201); B29C
48/0018 (20190201); B29C 55/28 (20130101); C08J
5/18 (20130101); B29C 48/022 (20190201); B29C
55/005 (20130101); C08F 210/16 (20130101); B29L
2023/001 (20130101); C08J 2423/08 (20130101); C08J
2323/08 (20130101); C08L 2203/16 (20130101); B29K
2023/08 (20130101); C08F 2500/05 (20130101); A01F
2015/0745 (20130101); C08F 2500/16 (20130101); A01F
15/0715 (20130101); C08L 2205/025 (20130101) |
Current International
Class: |
C08F
210/16 (20060101); B29C 48/00 (20190101); C08L
23/08 (20060101); B29C 55/00 (20060101); B29C
48/10 (20190101); C08J 5/18 (20060101); B29C
55/28 (20060101); A01F 15/07 (20060101) |
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Other References
International Search Report and Written Opinion issued for
International Application No. PCT/EP2017/060285, dated Jun. 12,
2017. cited by applicant.
|
Primary Examiner: Lee; Rip A
Attorney, Agent or Firm: Meunier Carlin & Curfman
LLC
Claims
The invention claimed is:
1. A machine direction oriented (MDO) monolayer film comprising a
multimodal copolymer of ethylene and at least two
alpha-olefin-comonomers having: a) a density of from 906 to 925
kg/m.sup.3 determined according to ISO 1183, b) an MFR.sub.21 of 10
to 200 g/10 min determined according to ISO1133, wherein the
multimodal copolymer of ethylene comprises c) a first copolymer of
ethylene and a first alpha-olefin comonomer having 4 to 10 carbon
atoms; and d) a second copolymer of ethylene having an alpha-olefin
comonomer different from that of the first copolymer, said second
alpha-olefin comonomer having 6 to 10 carbon atoms; and wherein the
machine directed oriented monolayer film has been stretched
uniaxially in the machine direction (MD) in a draw ratio of at
least 1:1.5.
2. The MDO monolayer film as claimed in claim 1 which has been
stretched uniaxially in the machine direction (MD) in a draw ratio
of at least 1:2.
3. The MDO monolayer film as claimed in claim 1 wherein the
multimodal copolymer of ethylene comprises 50 wt % or less of the
first copolymer of ethylene; 50 wt % or more of the second
copolymer of ethylene.
4. The MDO monolayer film as claimed in claim 1 wherein the first
copolymer of ethylene has i) a density of from 945 to 955
kg/m.sup.3; and ii) a melt flow rate MFR.sub.2 of 150 to 1500 g/10
min.
5. The MDO monolayer film as claimed in claim 1 wherein the second
copolymer of ethylene has a density of .ltoreq.903 kg/m.sup.3 when
calculated according to Equation 5 based on values determined
according to ISO 1183:
.rho..sub.b=w.sub.1.rho..sub.1+w.sub.2.rho..sub.2 Equation 5, where
.rho. is density in kg/m.sup.3, w is weight fraction of component
in a mixture and subscripts b, 1 and 2 refer to the mixture b,
component 1 (first copolymer) and component 2 (second copolymer),
respectively.
6. The MDO monolayer film as claimed in claim 1 wherein the second
copolymer of ethylene has MFR.sub.21 of <20 g/10 min when
calculated according to Equation 4: Hagstrom formula:
.times..times. ##EQU00004## where a=10.4, b=0.5 for MFR.sub.21, w
is the weight fraction of the polymer component having higher MFR,
MI.sub.b is the MFR.sub.21 of the second copolymer mixture,
MI.sub.1 is MFR.sub.21 of a first copolymer of ethylene, and
MI.sub.2 is MFR.sub.21 of the second copolymer of ethylene.
7. The MDO monolayer film as claimed in claim 1 having a thickness
of 10 to 30 microns after stretching.
8. The MDO monolayer film as claimed in claim 1 having one or more
of: an Elmendorf tear resistance of at least 310 N/mm in the TD; an
Elmendorf tear resistance of at least 90 N/mm in the MD; a
normalised peak force of 2000 to 3500 N/mm; a normalised energy to
peak force of 30 to 120 J/mm; and/or a normalised total penetration
energy of 30 to 90 J/mm.
9. The MDO monolayer film as claimed in claim 1 wherein the first
copolymer of ethylene has i) a density of from 945 to 955
kg/m.sup.3; and ii) a melt flow rate MFR2 of 150 to 1500 g/10
min.
10. A machine direction oriented (MDO) film comprising a multimodal
copolymer of ethylene and at least two alpha-olefin-comonomers
having: a) a density of from 906 to 925 kg/m.sup.3 determined
according to ISO 1183, b) an MFR.sub.21 of 10 to 200 g/10 min
determined according to ISO1133, wherein the multimodal copolymer
of ethylene comprises c) 35 to 50 wt % of a first copolymer of
ethylene comprising at least a first and a second fraction; said
first fraction comprising ethylene and a first alpha-olefin
comonomer having 4 to 10 carbon atoms and said second fraction
comprising ethylene and the first alpha-olefin comonomer having 4
to 10 carbon atoms said first and second fraction are present in a
weight ratio of 2:1 up to 1:2; and d) 50 to 65 wt % of a second
copolymer of ethylene having an alpha-olefin comonomer different
from the first copolymer, said second alpha-olefin comonomer having
6 to 10 carbon atoms; and wherein the machine directed oriented
film has been stretched uniaxially in the machine direction (MD) in
a draw ratio of at least 1:1.5.
11. A machine direction oriented (MDO) film according to claim 10,
wherein component (d) comprises a second copolymer of ethylene
having an alpha-olefin comonomer different from the first copolymer
having a density of below 900 kg/m.sup.3 when calculated according
to Equation 5, based on values determined according to ISO 1183:
.rho..sub.b=w.sub.1.rho..sub.1+w.sub.2.rho..sub.2 Equation 5, where
.rho. is density in kg/m.sup.3, w is weight fraction of component
in a mixture and subscripts b, 1 and 2 refer to the mixture b,
component 1 (first copolymer) and component 2 (second copolymer),
respectively.
12. The MDO film as claimed in claim 10 wherein the first and the
second fraction of the first copolymer of ethylene are produced in
two consecutive steps.
13. The MDO film as claimed in claim 10 which has been stretched
uniaxially in the machine direction (MD) in a draw ratio of at
least 1:2.
14. The MDO film as claimed in claim 10 wherein the second
copolymer of ethylene has a density of from .ltoreq.903 kg/m.sup.3
when calculated according to Equation 3 based on values determined
according to ISO 1183: .tau..times..times. ##EQU00005## where .tau.
is residence time Vr is volume of the reaction space and Qo is
volumetric flow rate of a product stream.
15. The MDO film as claimed in claim 10 wherein the second
copolymer of ethylene has MFR.sub.21 of <20 g/10 min when
calculated according to Equation 4: .times..times. ##EQU00006##
where a=10.4, b=0.5 for MFR.sub.21, w is the weight fraction of a
polymer component having higher MFR, MI.sub.b is the MFR.sub.21 of
the second copolymer mixture, MI.sub.1 is MFR.sub.21 of the first
copolymer of ethylene, and MI.sub.2 is MFR.sub.21 of the second
copolymer of ethylene.
16. The MDO film as claimed in claim 10 having one or more of: an
Elmendorf tear resistance of at least 375 N/mm in the TD; an
Elmendorf tear resistance of at least 100 N/mm in the MD; a
normalised peak force of 2250 to 2750 N/mm; a normalised energy to
peak force of 50 to 120 J/mm and/or a normalised total penetration
energy of 35 to 80 J/mm.
17. A process for the preparation of the machine direction oriented
film as claimed in claim 10 comprising: in a first reactor
polymerising ethylene and a first alpha-olefin comonomer having 4
to 10 carbon atoms to produce a first polyethylene fraction; in a
second reactor and in the presence of the first polyethylene
fraction, polymerising ethylene and said first alpha-olefin
comonomer having 4 to 10 carbon atoms to produce a second
polyethylene fraction, said first and second polyethylene fractions
forming a first copolymer of ethylene; in a third reactor and in
the presence of the first copolymer of ethylene, polymerising
ethylene and a second alpha-olefin comonomer different from the
first alpha-olefin comonomer, said second alpha-olefin comonomer
having 6 to 10 carbon atoms to produce a second copolymer of
ethylene; said first and second copolymers of ethylene forming a
multimodal copolymer of ethylene and at least two
alpha-olefin-comonomers having: a) a density of from 906 to 925
kg/m.sup.3 determined according to ISO 1183, b) an MFR.sub.21 of
10-200 g/10 min determined according to ISO1133, blowing said
multimodal copolymer of ethylene to form a first film; stretching
said first film in a machine direction in a draw ratio of at least
1:1.5.
18. The process as claimed in claim 17 wherein the second copolmer
of ethylene does not contain a residue of an alpha olefin with
fewer than 6 carbons atoms or wherein there is at least one alpha
olefin present in the second copolmer of ethylene which is
different from any alpha olefin present in said first copolymer of
ethylene.
Description
The present invention is directed to a MDO film comprising a
multimodal polyethylene copolymer comprising a first copolymer of
ethylene and a second copolymer of ethylene, said multimodal
polyethylene copolymer comprising at least two alpha-olefin
comonomers. In particular, the invention relates to the formation
of a MDO film suited for silage formation which has excellent
toughness and tear resistance. The invention also provides a
process for forming these machine direction oriented films and
silage packaged within such a film.
BACKGROUND OF THE INVENTION
This invention relates to films designed for the manufacture of
silage. Silage is fermented, high-moisture stored fodder which can
be fed to cattle, sheep and other such ruminants. It is fermented
and stored in a process called ensilage, ensiling or silaging, and
is usually made from grass crops, including maize, sorghum or other
cereals, using the entire green plant (not just the grain). Silage
can be made from many field crops. Silage is typically prepared by
placing cut green vegetation in a silo or pit, by piling it in a
large heap and compressing it down so as to leave as little oxygen
as possible and then covering it with a plastic sheet.
Alternatively, the material is tightly wrapped by a plastic film in
large round bales. The films of the present invention can be used
as covering films but ideally are used in bale formation.
The silage films of this invention allow generation of the aerobic
conditions necessary for silage fermentation. They enable the bales
to maintain high energy and nutrition value in the silage.
The film must also be able to withstand the rigours of baling. It
will be appreciated that a baling machine is used to prepare square
or round bales of grass crop which turns into silage. The bailer
puts a large stress on any film it employs. As the bale exits the
baler it falls onto a field covered in recently cut crop stubble
which can pierce the film. Bales are often stacked putting further
stress on the film and so on. Bales might be lifted using a
pitchfork or mechanical lifter, again stressing the film.
Stretch film efficiency is therefore a combination of film
performance needs, such as: stretch strength and load retention,
excellent tear resistance, excellent puncture resistance and
toughness, bespoke tack/cling, oxygen and water barrier, UV
stabilization, opacity and colour density. It is also important
that the film has operational efficiency at the stretch wrapper,
such as higher meters of film per reel to reduce downtime and reel
changes.
Higher meters per reel is achieved through down gauging of the film
with pre-stretching being the most advanced film process set up to
achieve it. The challenge with stretching however, is the ability
to keep film performance, such as tear resistance and toughness
while reducing the film thickness.
Films of use in the invention therefore need to perform in a
difficult environment. Toughness and tear resistance requirements
include: Reduction of breakages at the start of the bale wrapping
cycle (time saving) Ensuring efficient wrapping on both round &
square bales across variety of crops on all types of bale wrappers.
High Tear Resistance required both before & after
pre-stretching; Withstanding the forces of ejection from the
turntable onto sharp crop stubble recently cut (& combat their
damage), Withstanding rigorous bale handling or pick up by modern,
complex wrapping machinery; Stacking and stocking afterwards to
withstand piercing dry stalks and angular corners of square bales
and combat damage from birds, rodents, domestic pets etc. on
storage; Resisting the elements.
We have now found a particular multimodal copolymer is ideal for
making MDO films suitable for silage production.
The polymer used in the films itself is not new and similar
polymers are known in the art for other applications.
EP2883887 discloses a multimodal ethylene copolymer prepared in
three stages using Ziegler Natta catalysis. The target films are
used in food applications. There is no suggestion of orientation of
the films.
US2012/0238720 describes multimodal copolymers which are employed
in films with good optics.
EP2067799 describes monolayer or multilayer films with excellent
impact strength based on multimodal LLDPE.
There is however no suggestion of the use of multimodal films we
claim in oriented form and their suitability for use in the
manufacture of silage.
SUMMARY OF INVENTION
Viewed from one aspect the invention provides a machine direction
oriented film comprising a multimodal copolymer of ethylene and at
least two alpha-olefin-comonomers having: a) a density of from 906
to 925 kg/m.sup.3 determined according to ISO 1183, b) an
MFR.sub.21 of 10-200 g/10 min determined according to ISO 133,
wherein the multimodal copolymer of ethylene comprises c) a first
copolymer of ethylene and a first alpha-olefin comonomer having 4
to carbon atoms; and d) a second copolymer of ethylene having an
alpha-olefin comonomer different from the first copolymer, said
second alpha-olefin comonomer having 6 to 10 carbon atoms.
It is preferred if component d) does not contain the residue of an
alpha olefin with fewer than 6 carbons atoms. It is preferred if
there is at least one alpha olefin present in the component d)
which is different from any alpha olefin present in component
c).
MDO films are preferably stretched uniaxially in the machine
direction (MD) in a draw ratio of at least 1:1.5, such as at least
1:2.
Viewed from another aspect the invention provides a machine
direction oriented film comprising a multimodal copolymer of
ethylene and at least two alpha-olefin-comonomers having: a) a
density of from 906 to 925 kg/m.sup.3 determined according to ISO
1183, b) an MFR.sub.21 of 10-200 g/10 min determined according to
ISO1133,
wherein the multimodal copolymer of ethylene comprises c) a first
copolymer of ethylene comprising at least a first and a second
fraction; said first fraction comprising ethylene and a first
alpha-olefin comonomer having 4 to 10 carbon atoms and said second
fraction comprising ethylene and the first alpha-olefin comonomer
having 4 to 10 carbon atoms; and d) a second copolymer of ethylene
having an alpha-olefin comonomer different from the first
copolymer, said second alpha-olefin comonomer having 6 to 10 carbon
atoms.
Viewed from another aspect the invention provides a machine
direction oriented film comprising a multimodal copolymer of
ethylene and at least two alpha-olefin-comonomers having: a) a
density of from 906 to 925 kg/m.sup.3 determined according to ISO
1183, b) an MFR.sub.21 of 10-200 g/10 min determined according to
ISO1133,
wherein the multimodal copolymer of ethylene comprises c) a first
copolymer of ethylene comprising at least a first and a second
fraction; said first fraction comprising ethylene and a first
alpha-olefin comonomer having 4 to 10 carbon atoms and said second
fraction comprising ethylene and the first alpha-olefin comonomer
having 4 to 10 carbon atoms; and d) a second copolymer of ethylene
having an alpha-olefin comonomer different from the first
copolymer, said second alpha-olefin comonomer having 6 to 10 carbon
atoms having a density of below 900 kg/m.sup.3 when calculated
according to Equation 5, based on values determined according to
ISO 1183.
Viewed from another aspect the invention provides the use of a MDO
film as hereinbefore defined in packaging silage.
Viewed from another aspect the invention provides a process for the
formation of a MDO film as hereinbefore defined comprising blowing
a multimodal copolymer of ethylene and at least two
alpha-olefin-comonomers having: a) a density of from 906 to 925
kg/n determined according to ISO 1183, b) an MFR.sub.21 of 10-200
g/10 min determined according to ISO1133,
wherein the multimodal copolymer of ethylene comprises c) a first
copolymer of ethylene and a first alpha-olefin comonomer having 4
to carbon atoms; and d) a second copolymer of ethylene having an
alpha-olefin comonomer different from the first copolymer, said
second alpha-olefin comonomer having 6 to 10 carbon atoms;
so as to form a first film;
stretching said first film in the machine direction in a draw ratio
of at least 1:1.5.
Viewed from another aspect the invention provides a process for the
preparation of a machine direction oriented film comprising:
in a first reactor polymerising ethylene and a first alpha-olefin
comonomer having 4 to 10 carbon atoms so as to produce a first
polyethylene fraction;
in a second reactor and in the presence of the first polyethylene
fraction, polymerising ethylene and said first alpha-olefin
comonomer having 4 to 10 carbon atoms so as to produce a second
polyethylene fraction, said first and second polyethylene fractions
forming a first copolymer of ethylene;
in a third reactor and in the presence of the first copolymer of
ethylene, polymerising ethylene and a second alpha-olefin comonomer
different from the first alpha-olefin comonomer, said second
alpha-olefin comonomer having 6 to 10 carbon atoms so as to produce
a second copolymer of ethylene;
said first and second copolymers of ethylene forming a multimodal
copolymer of ethylene and at least two alpha-olefin-comonomers
having: a) a density of from 906 to 925 kg/m.sup.3 determined
according to ISO 1183, b) an MFR.sub.21 of 10-200 g/10 min
determined according to ISO1133,
blowing said multimodal copolymer of ethylene as to form a first
film;
stretching said first film in the machine direction in a draw ratio
of at least 1:1.5.
Viewed from another aspect the invention comprises a bale
comprising silage or a precursor thereto packaged within a MDO film
as hereinbefore defined.
Definitions
The multimodal copolymer of use in this invention can generally be
regarded as an LLDPE. The term LLDPE means linear low density
polyethylene herein.
The films of the invention are uniaxially oriented in the machine
direction (MDO). They are preferably not biaxially oriented
films.
DETAILED DESCRIPTION OF INVENTION
This invention relates to an MDO film comprising a particular
multimodal copolymer. The use of this copolymer in MDO films has
enabled the formation of a film that is ideally suited for silage
formation.
Multimodal Ethylene Copolymer
By multimodal ethylene copolymer is meant a copolymer which
contains distinct components having different average molecular
weights, different contents of comonomer or both. Preferably, the
copolymer contains distinct components having different average
molecular weights. The multimodal copolymer of the present
invention is produced by copolymerizing ethylene and at least two
comonomers in two or more polymerization stages where the
polymerization conditions are sufficiently different to allow
production of different polymers in different stages.
The "first copolymer" is defined as the polymer produced in the
first polymerization step (preferably a loop reactor or loop
reactors). This first copolymer may comprise two or more fractions.
The fractions are further denominated as "first fraction of the
first copolymer", "second fraction of the first copolymer",
etc.
A "first copolymer mixture" is defined as sum of all polymer
fractions produced in the first polymerization step, i.e.
prepolymerization, any first or second fraction of the first
copolymer.
Similar a "second copolymer" is defined as the polymer produced in
the second polymerization step, differing from the first
polymerization step, preferably done in a gas-phase-reactor.
Similar, a "second copolymer mixture" is defined as sum of all
polymer fractions produced in the second polymerization step, i.e.
any first or second fraction of the first copolymer and the second
copolymer.
The multimodal ethylene copolymer of the invention is a copolymer
of ethylene and at least two alpha-olefin comonomers, whereby the
multimodal ethylene copolymer comprises a first copolymer of
ethylene and an alpha-olefin comonomer having from 4 to 10 carbon
atoms and a second copolymer of ethylene and an alpha-olefin
comonomer having from 6 to 10 carbon atoms. There must be at least
two different comonomers present, i.e. both components cannot be
ethylene hex-1-ene copolymers.
It is preferred if the comonomers present in the first and second
copolymers are different. Ideally any comonomer used in the first
copolymer is not used in the manufacture of the second
copolymer.
Preferably the multimodal ethylene copolymer is a copolymer of
ethylene and at least two comonomers selected from 1-butene,
1-hexene, and 1-octene.
It is further preferred that the multimodal ethylene copolymer is a
copolymer of ethylene and exactly two comonomers selected from
1-butene, 1-hexene, or 1-octene. Especially preferred is a
multimodal ethylene copolymer comprising a first copolymer
comprising ethylene and 1-butene, and a second copolymer comprising
ethylene and 1-hexene.
Even more preferred is a multimodal ethylene copolymer comprising a
first copolymer consisting of ethylene and 1-butene and a second
copolymer of ethylene consisting of ethylene and 1-hexene.
The multimodal ethylene copolymer has a final density p of from 906
to 925 kg/m.sup.3, preferably 910 to 925 kg/m.sup.3 and more
preferably from 913 to 923 kg/m.sup.3. The resins having densities
lower than 906 kg/m.sup.3 tend to be so sticky that their
production becomes problematic in a particle forming process. On
the other hand, the resins having a final density of more than 925
kg/m.sup.3 do not have the required balance of properties required
in the end use applications for the multimodal ethylene copolymer,
such as they are not sufficiently soft and they may have a too low
tear strength.
The multimodal ethylene copolymer has a melt flow rate MFR.sub.21
of 10-200 g/10 min, preferably from 20-150 g/10 min, such as 25-100
g/min, such as 28-80 g/10 min. The resins having an MFR.sub.21 of
less than 10 g/10 min tend to have too high melt viscosity so that
the throughput in a converting process may become restricted.
On the other hand, the resins having MFR.sub.21 of more than 200
g/10 min have too low melt strength for the end use applications.
In addition, the combination of a high melt index with a low
density of the resin often causes the resin particles to be sticky
and this causes problems in a particle forming process, such as
plugging and fouling of process equipment. In addition, the
multimodal ethylene copolymer can have a flow rate ratio
FRR.sub.2/15 of at least 15 or more, such as 20 or 23 or more.
Furthermore, it can have a flow rate ratio FRR.sub.21/5 in the
range of 15-40, preferably in the range of 20-35.
The multimodal ethylene copolymer preferably has a melt flow rate
MFR.sub.5 of 0.1-20 g/10 min, preferably from 0.5-10 g/10 min, such
as 0.5-8.0 g/min, especially 0.5-5.0 g/10 mi. The MFR.sub.5 is
preferably from 0.8 to 4.0 g/10 min.
First Copolymer
The first copolymer of ethylene comprises ethylene and a first
alpha-olefin comonomer having 4 to 10 carbon atoms, such as
I-butene, 1-hexene or 1-octene, more preferably 1-butene.
In a preferred embodiment the first copolymer consists of ethylene
and 1-butene. The first copolymer of ethylene preferably has a melt
flow rate MFR.sub.2 of from 150-1500 g/10 min, such as 150 to 1000
g/10 min, preferably from 150 to 750 g/10 min and more preferably
from 180 to 600 g/10 min. Furthermore, the first copolymer may have
a density of from 945 to 955 kg/m.sup.3, preferably from 945 to 953
kg/m.sup.3 and most preferably from 948 to 953 kg/m.sup.3.
The first copolymer of ethylene is ideally produced in a first
polymerization stage which is preferably a slurry polymerization.
The slurry polymerization usually takes place in an inert diluent,
typically a hydrocarbon diluent such as methane, ethane, propane,
n-butane, isobutane, pentanes, hexanes, heptanes, octanes etc., or
their mixtures. Preferably the diluent is a low-boiling hydrocarbon
having from 1 to 4 carbon atoms or a mixture of such hydrocarbons.
An especially preferred diluent is propane, possibly containing
minor amount of methane, ethane and/or butane.
The ethylene content in the fluid phase of the slurry may be from 1
to about 50% by mole, preferably from about 2 to about 20% by mole
and in particular from about 2 to about 10% by mole. The benefit of
having a high ethylene concentration is that the productivity of
the catalyst is increased but the drawback is that more ethylene
then needs to be recycled than if the concentration was lower.
The temperature in the first polymerization stage is typically from
60 to 100.degree. C., preferably from 70 to 90.degree. C. An
excessively high temperature should be avoided to prevent partial
dissolution of the polymer into the diluent and the fouling of the
reactor. The pressure is from 1 to 150 bar, preferably from 40 to
80 bar.
The slurry polymerization may be conducted in any known reactor
used for slurry polymerization. Such reactors include a continuous
stirred tank reactor and a loop reactor. It is especially preferred
to conduct the polymerization in a loop reactor. In such reactors
the slurry is circulated with a high velocity along a closed pipe
by using a circulation pump. Loop reactors are generally known in
the art and examples are given, for instance, in U.S. Pat. Nos.
4,582,816, 3,405,109, 3,324,093, EP-A-479186 and U.S. Pat. No.
5,391,654. It is thus preferred to conduct the first polymerization
stage as a slurry polymerization in one or more loop reactors, more
preferably in two consecutive loop reactors.
The slurry may be withdrawn from the reactor either continuously or
intermittently. A preferred way of intermittent withdrawal is the
use of settling legs where slurry is allowed to concentrate before
withdrawing a batch of the concentrated slurry from the reactor.
The use of settling legs is disclosed, among others, in U.S. Pat.
Nos. 3,374,211, 3,242,150 and EP-A-1310295. Continuous withdrawal
is disclosed, among others, in EP-A-891990, EP-A-1415999,
EP-A-1591460 and WO-A-2007/025640. The continuous withdrawal is
advantageously combined with a suitable concentration method, as
disclosed in EP-A-1310295 and EP-A-1591460. It is preferred to
withdraw the slurry from the first polymerization stage
continuously.
Hydrogen is introduced into the first polymerization stage for
controlling the MFR.sub.2 of the first copolymer. The amount of
hydrogen needed to reach the desired MFR depends on the catalyst
used and the polymerization conditions. The desired polymer
properties have been obtained in slurry polymerization in a loop
reactor with the molar ratio of hydrogen to ethylene of from 100 to
1000 mol/kmol (or mol/1000 mol) and preferably of from 200 to 800
mol/kmol.
The first alpha-olefin comonomer is introduced into the first
polymerization stage for controlling the density of the first
copolymer. As discussed above, the comonomer is an alpha-olefin
having from 4 to 10 carbon atoms, preferably 1-butene, 1-hexene or
1-octene, more preferably 1-butene. The amount of comonomer needed
to reach the desired density depends on the comonomer type, the
catalyst used and the polymerization conditions. The desired
polymer properties have been obtained with 1-butene as the
comonomer in slurry polymerization in a loop reactor with the molar
ratio of comonomer to ethylene of from 100 to 1000 mol/kmol (or
mol/1000 mol) and preferably of from 200 to 800 mol/kmol.
The average residence time in the first polymerization stage is
typically from to 120 minutes, preferably from 30 to 80 minutes. As
it is well known in the art the average residence time T can be
calculated from:
.times..times..times..times..tau..times..times. ##EQU00001## where
Vr is the volume of the reaction space (in case of a loop reactor,
the volume of the reactor, in case of the fluidized bed reactor,
the volume of the fluidized bed) and Qo is the volumetric flow rate
of the product stream (including the polymer product and the fluid
reaction mixture).
The production rate in the first polymerization stage is suitably
controlled with the catalyst feed rate. It is also possible to
influence the production rate by suitable selection of the monomer
concentration in the first polymerization stage. The desired
monomer concentration can then be achieved by suitably adjusting
the ethylene feed rate into the first polymerization stage.
According to the present invention, it is beneficial that the
particles of the first copolymer of ethylene and the first
alpha-olefin comonomer have a narrow distribution for the residence
time. This is seen to pose advantages in view of the homogeneity of
the particles, namely in view of a more homogenous catalyst
activity when producing the second copolymer in the subsequent
gas-phase-reactor, leading to a more even distribution of the
gas-phase-reactor-fraction in/around these particles and a lower
amount of easily extractable low-molecular-weight fractions.
Without being bound to any theory inventors believe, that a certain
minimum residence time in the first polymerization steps influences
the catalyst activity in the sense, that densities can be better
controlled in the subsequent gas-phase-reactor.
So the present inventors have identified a way to create a more
homogenous polymer fraction of the first copolymer of ethylene and
the first alpha-olefin comonomer by splitting the production
process and producing the first copolymer in two consecutive
polymerization stages, such as two loop reactors. The polymer
produced in each such polymerization stage or set of reaction
conditions in one reaction stage or in one polymerization reactor
is herewith denominated as "fraction of the first copolymer",
namely "first fraction of the first copolymer", "second fraction of
the first copolymer, etc.
It is thus preferred if the first copolymer is produced in two loop
reactors in series. The first loop reactor forms a first fraction
and the second loop reactor forms a second fraction of the first
copolymer component.
This split production mode leads to a more homogenous residence
time of the particles of the first copolymer of ethylene and the
first alpha-olefin comonomer when entering the second
polymerisation stage (typically in GPR) and hence more uniform
properties of the particles produced in the second polymerization
step, i.e. gas-phase-reactor, in view of viscosity and density.
These two properties, namely viscosity and density in combination,
have then decisive influence on the final properties of the final
multimodal copolymer of ethylene and any articles produced
thereof.
Inventors also identified, that the more uniform properties of the
particles produced in the first copolymerization step are further
essential to achieve very low densities in the GPR in combination
with low MFR of the second ethylene copolymer produced in the
GPR.
So in a special embodiment the multimodal ethylene copolymer of the
present invention comprises a first and a second copolymer of
ethylene as mentioned above, wherein the first copolymer of
ethylene comprises at least a first and a second fraction.
These two or more fractions of the first copolymer of ethylene may
be unimodal in view of their molecular weight and/or their density
or they can be bimodal in respect of their molecular weight and/or
their density.
It is preferred that the two or more fractions of the first
copolymer are unimodal in view of their molecular weight and
density. This first and second fraction (and any further fraction)
of the first copolymer of ethylene and the first alpha-olefin
comonomer can be produced by any of the known process in the
art.
However it is preferred, that both fractions are produced with the
same technology, especially by applying the same method and
polymerization settings as disclosed with the "first
copolymer"-section above.
It is within the scope of the invention, that the first and the
second fraction of the first copolymer of ethylene and the first
alpha-olefin comonomer are present in a ratio of 4:1 up to 1:4,
such as 3:1 to 1:3, or 2:1 to 1:2, or 1:1.
It is further preferred, that the two or more fractions of the
first copolymer of ethylene are produced in two or more consecutive
reactors according to the same process and method as given further
above under "First copolymer".
For a person skilled in the art it will be clear that--when
producing the first and the second fraction of the first copolymer
of ethylene and the first alpha-olefin comonomer in two consecutive
reactors, there can (or even has to) be a certain difference in the
MFR.sub.2-values and density-values of each fraction.
It is hence understood within the meaning of the invention,
that--given the preferred MFR-range of 150 to 1500 g/10 min--both
the MFR.sub.2 after loop 1 and after loop2 of the first copolymer
of ethylene are to be within the range of 150-1500 g/10 mi.
Further, the MFR.sub.2 after loop2 can be up to double or 1.5 times
the MFR.sub.2 after loop1 or can be the same. Ideally, the MFR
increases from first to second fraction. Accordingly it is
understood within the scope of the invention, that--at the density
range in between 945 and 955 kg/m.sup.3--the densities of the first
and after the second (and after any further) fraction of the first
copolymer may differ by at most 3 kg/m.sup.3 and still be
understood as having been produced with the same process
condition.
Example
TABLE-US-00001 Loop density after 1 Loop density after loop 2 950
953 Same condition 954 951 Same condition 955 950 Different
condition
All fractions of the first copolymer are copolymeric and are
ideally based on the same comonomer(s). In a preferred embodiment
therefore the first fraction is an ethylene butene copolymer and
the second fraction is an ethylene butene copolymer.
Second Copolymer
The second copolymer of ethylene comprises ethylene and a second
alpha-olefin comonomer having 6 to 10 carbon atoms, such as
1-hexene or 1-octene, more preferably 1-hexene.
It is further preferred that the second alpha-olefin comonomer has
more carbon atoms than the first alpha-olefin monomer.
It is further preferred that the second alpha-olefin comonomer has
2 more carbon atoms than the first alpha-olefin monomer.
In a preferred embodiment the second copolymer consists of ethylene
and 1-hexene.
Without being bound to any theory the present inventors consider
that the use of alpha-olefin comonomers having 6 to 10 carbon atoms
facilitates the creation of tie-molecules already at lower
molecular weight than it would be possible with lower alpha-olefin
comonomer such as 1-butene. This easier formation of tie-molecules
has significant benefits when it comes to mechanical
properties.
The second copolymer is produced in the presence of any previously
produced polymer component, i.e. in the presence of at least the
first copolymer of ethylene, optionally any fractions of the first
copolymer and any prepolymerization-components, forming the
so-called "second copolymer mixture".
It is well understood for a person skilled that the density or
viscosity (MFR.sub.21) of the second copolymer as such cannot be
measured because the second copolymer cannot be isolated out of the
second copolymer mixture and from the first copolymer.
However, the MFR.sub.21 of the second copolymer can be calculated
by using the so called Hagstrom equation (Hagstrom, The Polymer
Processing Society, Europe/Africa Region Meeting, Gothenburg,
Sweden, Aug. 19-21, 1997).
.times..times..times..times..times..times..times..times.
##EQU00002##
As proposed by Hagstrom, a=10.4 and b=0.5 for MFR.sub.21. Further,
unless other experimental information is available,
MFR.sub.21/MFR.sub.2 for one polymer component (i.e. first
copolymer or second copolymer) can be taken as 30. Furthermore, w
is the weight fraction of the polymer component having higher MFR.
The first copolymer can thus be taken as the component 1 and the
second copolymer as the component 2. The MFR.sub.21 of the second
copolymer (MI2) can then be solved from equation 1 when the MFR21
of the first copolymer mixture (MI1) and the second copolymer
mixture (MIb) are known.
Preferably the second copolymer of ethylene and a second alpha
olefin comonomer has an MFR.sub.21 of <20 g/0 min when
calculated according to Equation 4: Hagstrom formula.
The content of the comonomer in the second copolymer is controlled
to obtain the desired density of the second copolymer mixture.
The density of the second copolymer cannot be directly measured.
However, by using the standard mixing rule of Equation 5 the
density of the second copolymer can be calculated starting from the
densities of the final copolymer and the first copolymer. Then the
Subscripts b, 1 and 2 refer to the overall mixture b (=second
copolymer mixture), component 1 (=first copolymer) and component 2
(=second copolymer), respectively.
.rho..sub.b=w.sub.1.rho..sub.1+w.sub.2.rho..sub.2 Equation 5:
Density mixing rule
where .rho. is the density in kg/m.sup.3, w is the weight fraction
of the component in the mixture and subscripts b, 1 and 2 refer to
the overall mixture b, component 1 and component 2,
respectively.
Within the scope of the invention is advantageous, that the density
of the second copolymer is lower than the density of the first
copolymer.
It is preferred, that the density of the second copolymer is below
900 kg/m.sup.3, such as at most 898 kg/m.sup.3, or 897 kg/m.sup.3
or below, or 895 kg/m.sup.3 or below or 892 kg/m.sup.3 or below, or
890 kg/m.sup.3 or below when calculated according to Equation
5.
Further within the scope of the invention it is preferred, that the
density of the second copolymer is at least 880 kg/m.sup.3, such as
at least 883 kg/m.sup.3 or at least 885 kg/m.sup.3. It is further
preferable, that the density of the second copolymer is within the
range of 880-<900.0 kg/m.sup.3, such as 885-898 kg/m.sup.3, such
as 885-897 kg/m.sup.3.
It is therefore preferred if the a second copolymer of ethylene
comprises a second alpha-olefin comonomer having 6 to 10 carbon
atoms, and has a density of below 900 kg/m.sup.3 when calculated
according to Equation 5, based on values determined according to
ISO 1183.
The ratio (i.e. the split) between the first and the second
copolymer within the final multimodal copolymer of ethylene and at
least two alpha-olefin-comonomers has significant effect on the
mechanical properties of the final composition.
It is hence envisaged within the scope of the invention that the
second copolymer of ethylene forms a significant part of the
polymer fractions present in the multimodal ethylene copolymer,
i.e. at least 50 wt. % of the final composition, preferably 53 wt.
% or more, such as 55 wt. % or more. More preferably the second
copolymer of ethylene may form about 60 wt. % or more, such as 65
wt. % or more of the multimodal copolymer of the present invention.
The second copolymer of ethylene may form up to 70 wt % of the
multimodal copolymer of the present invention.
Consecutively the first copolymer of ethylene forms at most 50 wt.
% or less of the multimodal ethylene copolymer of the current
invention, preferably 47 wt. % or less, such as 45 wt. % or less.
More preferably the first copolymer of ethylene may form about 40
wt. % or less, such as 35 wt. % of the multimodal copolymer of the
present invention. The first copolymer of ethylene preferably forms
at least 30 wt % of the multimodal copolymer of the present
invention.
Hydrogen feed is adjusted to achieve a desired melt flow rate (or
molecular weight) of the second copolymer mixture. Suitably the
hydrogen feed is controlled to maintain constant hydrogen to
ethylene ratio in the reaction mixture. The actual ratio depends on
the catalyst as well as the type of the polymerization. The desired
polymer properties have been obtained in gas phase polymerization
in a fluidized bed reactor by maintaining the ratio within the
range of from 1 to 20 mol/kmol, preferably from 1 to 10
mol/kmol.
The second alpha-olefin comonomer is typically introduced to
maintain a constant comonomer to ethylene ratio in the reaction
mixture. The comonomer to ethylene ratio that is needed to produce
a polymer with the desired density depends, among others, on the
type of comonomer and the type of catalyst. With 1-hexene as a
comonomer the desired polymer properties have been obtained in gas
phase polymerization in a fluidized bed reactor with a molar ratio
of 1-hexene to ethylene of from 500 to 1000 mol/kmol, preferably
from 600 to 950 mol/kmol and in particular from 650 to 950
mol/kmol.
Preferably the second polymerization stage is conducted as a
fluidized bed gas phase polymerization. In a fluidized bed gas
phase reactor an olefin is polymerized in the presence of a
polymerization catalyst in an upwards moving gas stream. The
reactor typically contains a fluidized bed comprising the growing
polymer particles containing the active catalyst located above a
fluidization grid.
The polymer bed is fluidized with the help of the fluidization gas
comprising the olefin monomer, eventual comonomer(s), eventual
chain growth controllers or chain transfer agents, such as
hydrogen, and eventual inert gas. The fluidization gas is
introduced into an inlet chamber at the bottom of the reactor. To
make sure that the gas flow is uniformly distributed over the
cross-sectional surface area of the inlet chamber the inlet pipe
may be equipped with a flow dividing element as known in the art,
e.g. U.S. Pat. No. 4,933,149 and EP-A-684871. One or more of the
above-mentioned components may be continuously added into the
fluidization gas to compensate for losses caused, among other, by
reaction or product withdrawal.
From the inlet chamber the gas flow is passed upwards through a
fluidization grid into the fluidized bed. The purpose of the
fluidization grid is to divide the gas flow evenly through the
cross-sectional area of the bed. Sometimes the fluidization grid
may be arranged to establish a gas stream to sweep along the
reactor walls, as disclosed in WO-A-2005/087361. Other types of
fluidization grids are disclosed, among others, in U.S. Pat. No.
4,578,879, EP600414 and EP-A-721798. An overview is given in
Geldart and Bayens: The Design of Distributors for Gas-fluidized
Beds, Powder Technology, Vol. 42, 1985.
The fluidization gas passes through the fluidized bed. The
superficial velocity of the fluidization gas must be higher that
minimum fluidization velocity of the particles contained in the
fluidized bed, as otherwise no fluidization would occur. On the
other hand, the velocity of the gas should be lower than the onset
velocity of pneumatic transport, as otherwise the whole bed would
be entrained with the fluidization gas. The minimum fluidization
velocity and the onset velocity of pneumatic transport can be
calculated when the particle characteristics are known by using
common engineering practice. An overview is given, among others in
Geldart: Gas Fluidization Technology, J. Wiley & Sons,
1986.
When the fluidization gas is contacted with the bed containing the
active catalyst the reactive components of the gas, such as
monomers, comonomers and chain transfer agents, react in the
presence of the catalyst to produce the polymer product. At the
same time the gas is heated by the reaction heat.
The unreacted fluidization gas is removed from the top of the
reactor and cooled in a heat exchanger to remove the heat of
reaction. The gas is cooled to a temperature which is lower than
that of the bed to prevent the bed from heating because of the
reaction. It is possible to cool the gas to a temperature where a
part of it condenses. When the liquid droplets enter the reaction
zone they are vaporised. The vaporisation heat then contributes to
the removal of the reaction heat. This kind of operation is called
condensed mode and variations of it are disclosed, among others, in
WO-A-2007/025640, U.S. Pat. No. 4,543,399, EP-A-699213 and
WO-A-94/25495. It is also possible to add condensing agents into
the recycle gas stream, as disclosed in EP-A-696293. The condensing
agents are non-polymerizable components, such as n-pentane,
isopentane, n-butane or isobutane, which are at least partially
condensed in the cooler.
The gas is then compressed and recycled into the inlet chamber of
the reactor. Prior to the entry into the reactor fresh reactants
are introduced into the fluidization gas stream to compensate for
the losses caused by the reaction and product withdrawal. It is
generally known to analyze the composition of the fluidization gas
and introduce the gas components to keep the composition constant.
The actual composition is determined by the desired properties of
the product and the catalyst used in the polymerization.
The catalyst may be introduced into the reactor in various ways,
either continuously or intermittently. Among others, WO-A-01/05845
and EP-A-499759 disclose such methods. Where the gas phase reactor
is a part of a reactor cascade the catalyst is usually dispersed
within the polymer particles from the preceding polymerization
stage. The polymer particles may be introduced into the gas phase
reactor as disclosed in EP-A-1415999 and WO-A-00/26258.
The polymeric product may be withdrawn from the gas phase reactor
either continuously or intermittently. Combinations of these
methods may also be used. Continuous withdrawal is disclosed, among
others, in WO-A-00/29452. Intermittent withdrawal is disclosed,
among others, in U.S. Pat. No. 4,621,952, EP-A-188125, EP-A-250169
and EP-A-579426.
The top part of the gas phase reactor may include a so called
disengagement zone. In such a zone the diameter of the reactor is
increased to reduce the gas velocity and allow the particles that
are carried from the bed with the fluidization gas to settle back
to the bed.
The bed level may be observed by different techniques known in the
art. For instance, the pressure difference between the bottom of
the reactor and a specific height of the bed may be recorded over
the whole length of the reactor and the bed level may be calculated
based on the pressure difference values. Such a calculation yields
a time-averaged level. It is also possible to use ultrasonic
sensors or radioactive sensors. With these methods instantaneous
levels may be obtained, which of course may then be averaged over
time to obtain a time-averaged bed level.
Also antistatic agent(s) may be introduced into the gas phase
reactor if needed. Suitable antistatic agents and methods to use
them are disclosed, among others, in U.S. Pat. Nos. 5,026,795,
4,803,251, 4,532,311, 4,855,370 and EP-A-560035. They are usually
polar compounds and include, among others, water, ketones,
aldehydes and alcohols.
The reactor may also include a mechanical agitator to further
facilitate mixing within the fluidized bed. An example of suitable
agitator design is given in EP-A-707513.
Typically the fluidized bed polymerization reactor is operated at a
temperature within the range of from 50 to 100.degree. C.,
preferably from 65 to 90.degree. C. The pressure is suitably from
10 to 40 bar, preferably from 15 to 30 bar. The average residence
time in the third polymerization stage is typically from 40 to 240
minutes, preferably from 60 to 180 minutes.
Prepolymerization
The polymerization steps discussed above may be preceded by a
prepolymerization step. The purpose of the prepolymerization is to
polymerize a small amount of polymer onto the catalyst at a low
temperature and/or a low monomer concentration. By
prepolymerization it is possible to improve the performance of the
catalyst in slurry and/or modify the properties of the final
polymer. The prepolymerization step is conducted in slurry.
Thus, the prepolymerization step may be conducted in a loop
reactor. The prepolymerization is then preferably conducted in an
inert diluent, typically a hydrocarbon diluent such as methane,
ethane, propane, n-butane, isobutane, pentanes, hexanes, heptanes,
octanes etc., or their mixtures. Preferably the diluent is a
low-boiling hydrocarbon having from 1 to 4 carbon atoms or a
mixture of such hydrocarbons.
The temperature in the prepolymerization step is typically from 0
to 90.degree. C., preferably from 20 to 80.degree. C. and more
preferably from 55 to 75.degree. C.
The pressure is not critical and is typically from 1 to 150 bar,
preferably from 40 to 80 bar. The amount of monomer is typically
such that from about 0.1 to 1000 grams of monomer per one gram of
solid catalyst component is polymerized in the prepolymerization
step. As the person skilled in the art knows, the catalyst
particles recovered from a continuous prepolymerization reactor do
not all contain the same amount of prepolymer. Instead, each
particle has its own characteristic amount which depends on the
residence time of that particle in the prepolymerization reactor.
As some particles remain in the reactor for a relatively long time
and some for a relatively short time, then also the amount of
prepolymer on different particles is different and some individual
particles may contain an amount of prepolymer which is outside the
above limits. However, the average amount of prepolymer on the
catalyst typically is within the limits specified above.
The molecular weight of the prepolymer may be controlled by
hydrogen as it is known in the art. Further, antistatic additive
may be used to prevent the particles from adhering to each other or
the walls of the reactor, as disclosed in WO-A-96/19503 and
WO-A-96/32420.
The catalyst components are preferably all introduced to the
prepolymerization step when a prepolymerization step is present.
However, where the solid catalyst component and the cocatalyst can
be fed separately it is possible that only a part of the cocatalyst
is introduced into the prepolymerization stage and the remaining
part into subsequent polymerization stages. Also in such cases it
is necessary to introduce so much cocatalyst into the
prepolymerization stage that a sufficient polymerization reaction
is obtained therein. It is understood within the scope of the
invention, that the amount or polymer produced in the
prepolymerization lies within 1-5 wt. % in respect to the final
multimodal copolymer.
Catalyst
The polymerization is conducted in the presence of an olefin
polymerization catalyst. The catalyst may be any catalyst which is
capable of producing the desired ethylene polymer. Suitable
catalysts are, among others, Ziegler-Natta catalysts based on a
transition metal, such as titanium, zirconium and/or vanadium
catalysts. Ziegler Natta catalysts are useful as they can produce
polymers within a wide range of molecular weight with a high
productivity.
Ziegler-Natta catalysts are preferred within the scope of the
invention. Suitable Ziegler-Natta catalysts preferably contain a
magnesium compound, an aluminium compound and a titanium compound,
optionally supported on a particulate support. The particulate
support can be an inorganic oxide support, such as silica, alumina,
titania, silicaalumina and silica-titania. Preferably, the support
is silica.
The average particle size of the silica support can be typically
from 10 to 100 .mu.m. However, it has turned out that special
advantages can be obtained if the support has median particle size
from 6 to 40 .mu.m, preferably from 6 to 30 .mu.m. The magnesium
compound is a reaction product of a magnesium dialkyl and an
alcohol. The alcohol is a linear or branched aliphatic monoalcohol.
Preferably, the alcohol has from 6 to 16 carbon atoms. Branched
alcohols are especially preferred, and 2-ethyl-1-hexanol is one
example of the preferred alcohols. The magnesium dialkyl may be any
compound of magnesium bonding to two alkyl groups, which may be the
same or different. Butyl-octyl magnesium is one example of the
preferred magnesium dialkyls.
The aluminium compound is chlorine containing aluminium alkyl.
Especially preferred compounds are aluminium alkyl dichlorides and
aluminium alkyl sesquichlorides.
The titanium compound is a halogen containing titanium compound,
preferably chlorine containing titanium compound. Especially
preferred titanium compound is titanium tetrachloride. The catalyst
can be prepared by sequentially contacting the carrier with the
above mentioned compounds, as described in EP-A-688794 or
WO-A-99/51646. Alternatively, it can be prepared by first preparing
a solution from the components and then contacting the solution
with a carrier, as described in WO-A-01/55230.
Another group of suitable Ziegler-Natta catalysts contain a
titanium compound together with a magnesium halide compound acting
as a support. Thus, the catalyst contains a titanium compound on a
magnesium dihalide, like magnesium dichloride. Such catalysts are
disclosed, for instance, in WO-A-2005/118655 and EP-A-810235. Still
a further type of Ziegler-Natta catalysts are catalysts prepared by
a method, wherein an emulsion is formed, wherein the active
components form a dispersed, i.e. a discontinuous phase in the
emulsion of at least two liquid phases. The dispersed phase, in the
form of droplets, is solidified from the emulsion, wherein catalyst
in the form of solid particles is formed.
The principles of preparation of these types of catalysts are given
in WO-A-2003/106510 of Borealis. The Ziegler-Natta catalyst is used
together with an activator. Suitable activators are metal alkyl
compounds and especially aluminium alkyl compounds. These compounds
include alkyl aluminium halides, such as ethylaluminium dichloride,
diethylaluminium chloride, ethylaluminium sesquichloride,
dimethylaluminium chloride and the like. They also include
trialkylaluminium compounds, such as trimethylaluminium,
triethylaluminium, tri-isobutylaluminium, trihexylaluminium and
tri-n-octylaluminium. Furthermore they include alkylaluminium
oxycompounds, such as methylaluminiumoxane (MAO),
hexaisobutylaluminiumoxane (HIBAO) and tetraisobutylaluminiumoxane
(TIBAO). Also other aluminium alkyl compounds, such as
isoprenylaluminium, may be used. Especially preferred activators
are trialkylaluminiums, of which triethylaluminium,
trimethylaluminium and tri-isobutylaluminium are particularly
useful.
The amount in which the activator is used depends on the specific
catalyst and activator. Typically triethylaluminium is used in such
amount that the molar ratio of aluminium to the transition metal,
like Al/Ti, is from 1 to 1000, preferably from 3 to 100 and in
particular from about 5 to about 30 mol/mol.
Film Preparation
Films are produced by extrusion through an annular die with a
pressure difference applied to blow the extruded cylinder into a
film and achieve the desired orientation within the film, i.e. to
build a stress into the cooled film.
For film formation the polymer is ideally intimately mixed with any
other components present prior to extrusion and blowing of the film
as is well known in the art. It is especially preferred to
thoroughly blend the components, for example using a twin screw
extruder, preferably a counter-rotating extruder prior to extrusion
and film blowing.
The films of the invention are uniaxially oriented. That means that
they are stretched in at least a single direction, the machine
direction. Ideally, the films are stretched in the machine
direction only.
The preparation of a uniaxially oriented multilayer film of the
invention comprises at least the steps of forming a layered film
structure and stretching the obtained multilayer film in a draw
ratio of at least 1:1.5, preferably at least 1:2. Maximum stretch
may be 1:6, such as 1:5.
Typically the compositions providing the layers of the film will be
blown i.e. (co)extruded at a temperature in the range 160.degree.
C. to 240.degree. C., and cooled by blowing gas (generally air) at
a temperature of 10 to 50.degree. C. to provide a frost line height
of 1 or 2 to 8 times the diameter of the die. The blow up ratio
should generally be in the range 1.2 to 6, preferably 1.5 to 4.
It is preferred if the film of the invention is a monolayer
film.
The obtained film is subjected to a subsequent stretching step,
wherein the film is stretched in the machine direction. Stretching
may be carried out by any conventional technique using any
conventional stretching devices which are well known to those
skilled in the art.
Stretching is preferably carried out at ambient temperature, such
as in the range 20-35.degree. C. e.g. about 20 to 25.degree. C. Any
conventional stretching rate may be used, e.g. 2 to 40%/second.
The film is stretched only in the machine direction to be uniaxial.
The effect of stretching in only one direction is to uniaxially
orient the film.
The film is stretched at least 1.5 times. This is stated herein as
a draw ratio of at least 1:1.5, i.e. "1" represents the original
length of the film and "1.5" denotes that it has been stretched to
1.5 times that original length. Preferred films of the invention
are stretched in a draw ratio of at least 1:2, more preferably
between 1:2 and 1:4, e.g. between 1:2 and 1:3. An effect of
stretching (or drawing) is that the thickness of the film is
similarly reduced. Thus a draw ratio of at least 1:3 preferably
also means that the thickness of the film is reduced to less than
the original thickness,
Blow extrusion and stretching techniques are well known in the art,
e.g. in EP-A-299750.
The film preparation process steps of the invention are known and
may be carried out in one film line in a manner known in the art.
Such film lines are commercially available.
The films of the invention typically have a starting (or original)
thickness of 100 m or less. The films should have a starting
thickness of at least 10 microns.
After stretching, the final thickness of the uniaxially oriented
films, of the invention is typically 8 .mu.m to 80 .mu.m, more
preferably 10 to 50 .mu.m, ideally 10 to 30 .mu.m.
Films
Films of the invention comprise the multimodal copolymer of
ethylene and at least two alpha-olefin comonomers as hereinbefore
defined. The films of the invention are monoaxially orientated in
the machine direction. Films according to the present invention may
be mono- or multilayer films, comprising one or more layers, such
as two, three or five layers, even up to seven, up to 9 or up to 12
layers. Monolayer films are preferred.
In multilayer films comprising the multimodal copolymer of ethylene
and at least two alpha olefin-comonomers according to the present
invention, the multimodal copolymer according to the present
invention may be contained by at least one of the layers.
It is within the scope of the present invention, that a monolayer
film may comprise 1-100 wt % of the multimodal copolymer according
to the present invention. It is also within the scope of the
invention that such monolayer film can comprise 10-90 wt. %, such
as 30-70 wt. %, or like 40-60 wt. % or 45-55 wt. % of the
multimodal copolymer.
However, a monolayer film comprising 80 to 100% of the multimodal
copolymer of the present invention is preferred, such as 80 to 98
wt %. It will be appreciated that the film may contain small
amounts of additives as is standard in the art and a film
comprising 100% of the polymer of the invention can contain such
additives.
It is further within the scope of the present invention, that each
layer of a multilayer film independently from the others may
comprise 1-100 wt. % of the multimodal copolymer according to the
present invention. It is preferred, that each layer independently
from the others comprises 10-98 wt. %, such as 30-70 wt. %, or like
40-60 wt. % or 45-55 wt. % of the multimodal copolymer according to
the present invention.
Film Properties
The films of the invention may have an Elmendorf tear resistance of
at least 310 N/mm in the TD, such as at least 375 N/mm.
The films of the invention may have an Elmendorf tear resistance of
at least 90 N/mm in the MD, such as at least 100 N/mm.
The films of the invention preferably have Normalised peak force of
2000 to 3500 N/mm, such as 2250 to 2750 N/mm.
Normalised energy to peak force may be 30 to 120 J/mm, such as 50
to 120 J/mm.
Normalised total penetration energy may be 30 to 90 J/mm, such as
35 to 80 J/mm.
It is within the scope of the present invention that the films of
the invention comprise additives as used in the art, such as
phenolic stabilizers, antioxidants, slip and antistatic agents,
antiblock agents processing aids etc.
Applications
The films of the invention are preferably used in packaging silage.
The invention therefore relates to a method for the manufacture of
silage comprising wrapping plant material such as green vegetation
in a film as hereinbefore defined so as to form a bale;
allowing the plant material to undergo anaerobic fermentation to
form silage.
The invention will now be described with reference to the following
non-limiting examples and figures.
FIG. 1 shows penetration energy values before stretching for the
polymers of the invention vs the prior art comparative examples and
then looks at values after stretching 1:2 and 1:3 times in the
machine direction.
FIG. 2 shows Elmendorf tear values before stretching for the
polymers of the invention vs the prior art comparative examples and
then looks at values after stretching 1:2 and 1:3 times in the
machine direction. Results are for MD tear.
FIG. 3 shows Elmendorf tear values before stretching for the
polymers of the invention vs the prior art comparative examples and
then looks at values after stretching 1:2 and 1:3 times in the
machine direction. Results are for TD tear.
DETERMINATION METHODS
Melt flow rate (MFR) was determined according to ISO 1133 at
190.degree. C. The load under which the measurement is conducted is
given as a subscript. Thus, the MFR under the load of 2.16 kg is
denoted as MFR2. The melt flow rate MFR21 is correspondingly
determined at 190.degree. C. under a load of 21.6 kg and MFR5 under
a load of 5 kg.
The melt index MFR is herein assumed to follow the mixing rule
given in Equation 4 (Hagstrom formula):
##EQU00003##
As proposed by Hagstrom, a=10.4 and b=0.5 for MFR21. Further,
unless other experimental information is available, MFR21/MFR2 for
one polymer component (i.e. first copolymer or second copolymer)
can be taken as 30. Furthermore, w is the weight fraction of the
polymer component having higher MFR. The first copolymer can thus
be taken as the component 1 and the second copolymer as the
component 2. The MFR21 of the second copolymer (MI2) can then be
solved from equation 1 when the MFR21 of the first copolymer
mixture (MI1) and the second copolymer mixture (MIb) are known.
It is herewith stated, that the following expressions are to be
understood as defined: "MFR2 loop1" is understood as the MFR of the
polymer available after the first loop, comprising the "first
fraction of the first copolymer" and optionally any polymer
fraction produced in the prepolymerization-step (if any).
"Density Loop1" is understood as the density of the polymer
available after the first loop, comprising the first fraction of
the first copolymer and optionally any polymer fraction produced in
the prepolymerization-step (if any).
"MFR2 loop2" or "MFR2 after loop2" is understood as the MFR of the
polymer available after the second loop, i.e. comprising the first
fraction of the first copolymer and the second fraction of the
first copolymer and optionally polymer produced in any
prepolymerization-step (if any).
The MFR2 of the polymer fraction produced in the second loop (i.e.
the second fraction of the first copolymer) is to be calculated
according to Equation 4: Hagstrom formula and denominates as "MFR2
of the second loop", i.e. the MFR2 of second fraction of the first
copolymer. Log MFR2(loop)=n*log MFI(split1)+(1-n)*log MFR(split2)
Equation 6: MFR mixing rule "Loop density after Loop2" (or "Density
Loop2) is understood as the density of the polymer available after
the second loop, i.e. comprising the first fraction of the first
copolymer and the second fraction of the first copolymer and
optionally polymer produced in any prepolymerization--step (if
any).
The density of the polymer fraction produced in the second loop
(i.e. the density of the second fraction of the first copolymer) is
to be calculated according to Equation 5: Density mixing rule
.rho..sub.b=w.sub.1.rho..sub.1+w.sub.2.rho..sub.2
"Final MFR21" is understood as the MFR of the polymer available
after the gas phase reactor (GPR), i.e. comprising all the polymer
fractions produced in any preceding polymerization step, i.e.
comprising the first fraction and the second fraction of the first
copolymer, the high molecular-weight fraction produced in the GPR
and optionally polymer produced in any prepolymerization-step (if
any). "GPR MFR2" denominates the MFR of the polymer fraction
produced in the GPR and is to be calculated according to Equation
4.
Density
Density of the polymer was measured according to ISO 1183-1:2004
Method A on compression moulded specimen prepared according to EN
ISO 1872-2 (February 2007) and is given in kg/m3. The density is
herein assumed to follow the mixing rule as given in Equation 5:
Density mixing rule
.rho..sub.b=w.sub.1.rho..sub.1+w.sub.2.rho..sub.2 Herein .rho. is
the density in kg/m3, w is the weight fraction of the component in
the mixture and subscripts b, 1 and 2 refer to the overall mixture
b, component 1 and component 2, respectively. "Density of GPR
(calc)" has been calculated according to Equation 5 accordingly.
Molecular Weights, Molecular Weight Distribution, Mn, Mw, MWD
The weight average molecular weight Mw and the molecular weight
distribution (MWD=Mw/Mn wherein Mn is the number average molecular
weight and Mw is the weight average molecular weight) is measured
by a method based on ISO 16014-4:2003. A Waters 150CV plus
instrument, equipped with refractive index detector and online
viscosimeter was used with 3.times.HT6E styragel columns from
Waters (styrene-divinylbenzene) and 1,2,4-trichlorobenzene (TCB,
stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as
solvent at 140.degree. C. and at a constant flow rate of 1 mL/min.
500 .mu.L of sample solution were injected per analysis. The column
set was calibrated using universal calibration (according to ISO
16014-2:2003) with 10 narrow MWD polystyrene (PS) standards in the
range of 1.05 kg/mol to 11 600 kg/mol. Mark Houwink constants were
used for polystyrene and polyethylene (K: 19.times.10.sup.-3 dL/g
and a: 0.655 for PS, and K: 39.times.10.sup.-3 dL/g and a: 0.725
for PE). All samples were prepared by dissolving 0.5-3.5 mg of
polymer in 4 mL (at 140.degree. C.) of stabilized TCB (same as
mobile phase) and keeping for 2 hours at 140.degree. C. and for
another 2 hours at 160.degree. C. with occasional shaking prior
sampling in into the GPC instrument.
Comonomer Determination (NMR Spectroscopy)
Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used
to quantify the comonomer content of the polymer Quantitative
13C{1H} NMR spectra recorded in the molten-state using a Bruker
Advance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz
for 1H and 13C respectively. All spectra were recorded using a 13C
optimised 7 mm magic-angle spinning (MAS) probehead at 150.degree.
C. using nitrogen gas for all pneumatics. Approximately 200 mg of
material was packed into a 7 mm outer diameter zirconia MAS rotor
and spun at 4 kHz. This setup was chosen primarily for the high
sensitivity needed for rapid identification and accurate
quantification. {[1], [2], [6]} Standard single-pulse excitation
was employed utilising the transient NOE at short recycle delays of
3 s {[1], [3]} and the RS-HEPT decoupling scheme {[4], [5]}. A
total of 1024 (1 k) transients were acquired per spectrum. This
setup was chosen due its high sensitivity towards low comonomer
contents. Quantitative 13C{1H} NMR spectra were processed,
integrated and quantitative properties determined using custom
spectral analysis automation programs. All chemical shifts are
internally referenced to the bulk methylene signal (S+) at 30.00
ppm {[9]}. Characteristic signals corresponding to the
incorporation of 1-hexene were observed {[9]} and all contents
calculated with respect to all other monomers present in the
polymer. H=I*B4
With no other signals indicative of other comonomer sequences, i.e.
consecutive comonomer incorporation, observed the total 1-hexene
comonomer content was calculated based solely on the amount of
isolated 1-hexene sequences: Htotal=H
Characteristic signals resulting from saturated end-groups were
observed. The content of such saturated end-groups was quantified
using the average of the integral of the signals at 22.84 and 32.23
ppm assigned to the 2 s and 2 s sites respectively:
S=(1/2)*(I2S+I3S)
The relative content of ethylene was quantified using the integral
of the bulk methylene (.delta.+) signals at 30.00 ppm:
E=(1/2)*I.delta.+
The total ethylene comonomer content was calculated based the bulk
methylene signals and accounting for ethylene units present in
other observed comonomer sequences or end-groups:
Etotal=+(5/2)*B+(3/2)*S
The total mole fraction of 1-hexene in the polymer was then
calculated as: fH=(Htotal/(Etotal+Htotal)
The total comonomer incorporation of 1-hexene in mole percent was
calculated from the mole fraction in the usual manner: H[mol
%]=100*fH
The total comonomer incorporation of 1-hexene in weight percent was
calculated from the mole fraction in the standard manner: H [wt
%]=100*(fH*84.16)/(fH*84.16)+((1-fH)*28.05)) [1] Klimke, K.,
Parkinson, M, Piel, C., Kaminsky, W., Spiess, Wilhelm, M.,
Macromol. Chem. Phys. 2006; 207:382. [2] Parkinson, M., Klimke, K.,
Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128.
[3] Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M.,
Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813.
[4] Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239
[5] Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown,
S. P., Mag. Res. in Chem. 2007 45, Si, S198 [6] Castignolles, P.,
Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50
(2009) 2373 [7] Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D.,
Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187
(2007) 225 [8] Busico, V., Carbonniere, P., Cipullo, R.,
Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun.
2007, 28, 1128 [9] J. Randall, Macromol. Sci., Rev. Macromol. Chem.
Phys. 1989, C29, 201. Draw Down Ratio (DDR):
Speed of the haul off/Speed of the extruder (represents MD
orientation)
It indicates the final thickness reduction in the melt after
blowing. It is the ratio between the speed of the haul off over the
speed of the extruder and often estimated by using the following
equation: DDR=Width of the die gap/(Film thickness.times.BUR)
A drawdown ratio greater than 1 indicates that the melt has been
pulled away from the die faster than it issued from the die. The
film has been thinned and possesses an orientation in the machine
direction (MD).
Blow Up Ratio (BUR):
Diameter of the bubble/Diameter of the die (represents TD
orientation)
BUR indicates the increase in the bubble diameter over the die
diameter. A blow-up ratio greater than 1 indicates the bubble has
been blown to a diameter greater than that of the die orifice. The
film has been thinned and possesses an orientation in the
transverse direction (TD).
Peak Force Penetration Energy
Determination of Instrumented Puncture Impact of the Films
According to ISO 7765-2:
The method used to assess the behavior of plastic films in impact
stress perpendicular to the film plane and allowed by electronic
acquisition of measured values, the energy absorption capacity, the
puncture force and the compare deformability of the films.
In order to assess the puncture impact properties of the plastic
film, the film specimen is punctured at its centre using a
non-lubricated striker, perpendicularly to the test-specimen
surface, at a nominally uniform velocity of 4.4 m/s and 23.degree.
C. The test specimen is clamped in position during the test
(support ring diameter of 40 mm). The force-deflection or
force-time diagram is recorded electronically by the instrumented
striker with a diameter of 20 mm. From these force-deflections
several features and parameters of the material behaviour can be
inferred, such as
Peak Force is the maximum force occurring during the test in
Newtons (N)
Deformation at peak force: is the deformation that occurs at the
peak force in millimetres (mm)
Energy to peak force is the area under the force-deflection curve
up to the deflection at peak force in Joules (J)
Total Penetration Energy: The total energy expended in penetrating
the test specimen in Joules (J)
For normalized values, the respective parameter is divided by the
film thickness in millimetres.
Tear resistance (determined as Elmendorf tear (N): Applies for the
measurement both in machine direction and in transverse direction.
The tear strength is measured using the ISO 6383/2 method. The
force required to propagate tearing across a film sample is
measured using a pendulum device. The pendulum swings under gravity
through an arc, tearing the specimen from pre-cut slit. The
specimen is fixed on one side by the pendulum and on the other side
by a stationary clamp. The tear resistance is the force required to
tear the specimen. The relative tear resistance (N/mm) is then
calculated by dividing the tear resistance by the thickness of the
film.
Catalyst Preparation
Complex Preparation:
87 kg of toluene was added into the reactor. Then 45.5 kg Bomag A
(Butyoctyl magnesium) in heptane was also added in the reactor. 161
kg 99.8% 2-ethyl-1-hexanol was then introduced into the reactor at
a flow rate of 24-40 kg/h. The molar ratio between BOMAG-A and
2-ethyl-1-hexanol was 1:1.83.
Solid Catalyst Component Preparation:
275 kg silica (ES747JR of Crossfield, having average particle size
of 20 .quadrature.m) activated at 600.degree. C. in nitrogen was
charged into a catalyst preparation reactor. Then, 411 kg 20% EADC
(2.0 mmol/g silica) diluted in 555 litres pentane was added into
the reactor at ambient temperature during one hour. The temperature
was then increased to 35.degree. C. while stirring the treated
silica for one hour. The silica was dried at 50.degree. C. for 8.5
hours. Then 655 kg of the complex prepared as described above (2
mmol Mg/g silica) was added at 23.degree. C. during ten minutes. 86
kg pentane was added into the reactor at 22.degree. C. during ten
minutes. The slurry was stirred for 8 hours at 50.degree. C.
Finally, 52 kg TiCl4 was added during 0.5 hours at 45.degree. C.
The slurry was stirred at 40.degree. C. for five hours. The
catalyst was then dried by purging with nitrogen.
Polymerization:
Inventive Examples IE1-IE2
A loop reactor having a volume of 50 d.sup.3 was operated at a
temperature of 70.degree. C. and a pressure of 63 bar. Into the
reactor were ethylene, 1-butene, propane diluent and hydrogen so
that the feed rate of ethylene was 2.0 kg/h, hydrogen was 5.0 g/h,
1-butene was 80 g/h and propane was 50 kg/h. Also 11 g/h of a solid
polymerization catalyst component produced as described above was
introduced into the reactor together with triethylaluminium
cocatalyst so that the molar ratio of Al/Ti was about 15. The
production rate was 1.9 kg/h. A stream of slurry was continuously
withdrawn and directed to a loop reactor having a volume of 150
dm.sup.3 and which was operated at a temperature of 85.degree. C.
and a pressure of 61 bar. Into the reactor were further fed
additional ethylene, propane diluent, 1-butene comonomer and
hydrogen so that the ethylene concentration in the fluid mixture
was 2.9-5.1% by mole, the hydrogen to ethylene ratio was 250-1000
mol/kmol, the 1-butene to ethylene ratio was 300-3300 mol/kmol and
the fresh propane feed was 41 kg/h. The production rate was 7-21
kg/h.
A stream of slurry from the reactor was withdrawn intermittently
and directed into a loop reactor having a volume of 350 dm3 and
which was operated at 85.degree. C. temperature and 54 bar
pressure. Into the reactor was further added fresh propane feed of
69 kg/h and ethylene, 1-butene and hydrogen so that the ethylene
content in the reaction mixture was 19-4.7 mol %, the molar ratio
of 1-butene to ethylene was 520-1260 mol/kmol and the molar ratio
of hydrogen to ethylene was 230-500 mol/kmol. The production rate
was 13-26 kg/h. The slurry was withdrawn from the loop reactor
intermittently by using settling legs and directed to a flash
vessel operated at a temperature of 50.degree. C. and a pressure of
3 bar. From there the polymer was directed to a fluidized bed gas
phase reactor operated at a pressure of bar and a temperature of
80.degree. C. Additional ethylene, 1-hexene comonomer, nitrogen as
inert gas and hydrogen were added so that the ethylene content in
the reaction mixture was 13-25 mol-%, the ratio of hydrogen to
ethylene was 4-33 mol/kmol and the molar ratio of 1-hexene to
ethylene was 7-370 mol/kmol. The polymer production rate in the gas
phase reactor was 43-68 kg/h and thus the total polymer withdrawal
rate from the gas phase reactor was about 115 kg/h. The polymer
powder was mixed under nitrogen atmosphere with 500 ppm of
Ca-stearate and 1200 ppm of Irganox B225. Then it was compounded
and extruded under nitrogen atmosphere to pellets by using a CIMP90
extruder so that the SEI was 230 kWh/ton and the melt temperature
260.degree. C.
The polymers in table 2 were converted into 25 .mu.m films on a
Collin monolayer film extruder applying a draw down ratio (DDR) of
30.
Machine-settings: L/D ratio: 30; die gap: 1.5 mm, die diameter: 60,
blow up ratio (BUR) 2.5; frost line height: 120 mm.
Temperature Profile:
MFR5>1.2-2.0: 80 160 180 180 180 180 180 180 180.degree. C.
MFR5>2.0-5.0: 80 150 160 160 160 160 160 160 160.degree. C.
The 25 micron films are then stretched in the machine direction at
a roller temperature of 22.degree. C. Stretching was carried out
using a monodirectional stretching machine manufactured by Hosokawa
Alpine AG in Augsburg/Germany. The film obtained from blown film
extrusion was pulled into the orientation machine then stretched
between two sets of nip rollers where the second pair runs at
higher speed than the first pair resulting in the desired draw
ratio. Stretching is carried out with the draw ratios presented in
Table 3. After exiting the stretching machine the film is fed into
a conventional film winder where the film is slit to its desired
width and wound to form reels.
TABLE-US-00002 TABLE 1 characteristics of materials used for the
study LLDPE Density, MFR5, MF material Modality Comonomer
kg/m.sup.3 g/10 min g/10 min. IE1 Bimodal C4-loops/ 920 1.9 C6-GPR
IE2 Bimodal C4-loops/ 917 2.3 C6-GPR Dowlex C8 920 1.0 2045S
FK1820A-02 Bimodal 918 1.5
TABLE-US-00003 TABLE 2 physical parameters reflecting the polymer
structure of LLDPE Parameters Unit IE1 IE2 Loop 1 density
kg/m.sup.3 951.8 951.9 Loop 1 MFR.sub.2 g/10 min 189 206 Loop 2
density kg/m.sup.3 952.1 953 Loop 2 MFR.sub.2 g/10 min 240 348 GPR
split % 58.1 58.1 GPR density kg/m.sup.3 896.9 891.4 Pellet density
kg/m.sup.3 920 917 Pellet MFR.sub.5 g/10 min 1.9 2.3
TABLE-US-00004 TABLE 3 IE1 IE2 Dowlex 2045S FK1820A-02 MFR2 1.0 1.5
MFR5 1.9 2.3 Density 920 917.2 920 918 Before MDO Stretching BUR --
1:2.5 1:2.5 1:2.5 1:2.5 Blown film thickness .mu.m 25 .mu.m 25
.mu.m 25 .mu.m 25 .mu.m melt T .degree. C. .degree. C. 223 222 228
230 melt pressure before bar 155 141 169 144 screw speed rpm 70 75
66 78 Take-off speed m/min 25.9 26.0 26.3 25.6 FLH, mm mm 700 600
700 700 Puncture, ISO 7765-2 Peak Force N 37.6 38.7 30.4 39.0
Deformation @ Peak Force mm 32.2 44 26.7 61.1 Total Penetration
Energy J 0.9 1.3 0.6 2.2 Film thickness mm 0.025 0.023 0.023 0.023
Normalised Peak Force N/mm 1505.7 1680.8 1322.7 1696.4 Normalized
Energy to Peak Force J/mm 32 51 23.5 76 Normalized Total
Penetration Energy J/mm 37.7 57 24.5 96.4 Tear Elmendorf, ISO6383-2
MD Relative Tear Resistance N/mm 37.97 40.87 111.55 136.2 Tear
Elmendorf, ISO6383-2 TD Relative Tear Resistance N/mm 315.75 321.17
239.63 160.45
TABLE-US-00005 TABLE 4 Film testing after MDO Stretching 1:2 IE1
IE2 Dowlex 2045S FK1820A-02 MDO Stretch 1:2 Initial thickness .mu.m
25 25 25 25 Final thickness .mu.m 18 20 17 20 Stretch Ratio 1:2 1:2
1:2 1:2 Initial Width mm 600 600 600 600 Final Width mm 350 350 350
350 T .degree. C. Stretching Roll .degree. C. 22 22 22 22 Puncture,
ISO7765-2 Peak Force N 39.1 39.2 23.9 26.1 Deformation @ Peak Force
mm 46.5 54.7 19.8 21.6 Total Penetration Energy J 1.3 1.4 0.4 0.4
Film thickness .mu.m 15 15 16 16 Normalised Peak Force N/mm 2610
2615.9 1491.9 1633.5 Normalized Energy to Peak Force J/mm 82.6 93.8
18.8 22.1 Normalized Total Penetration Energy J/mm 84.6 94.7 25.5
26 Tear Elmendorf, ISO6383-2 MD Relative Tear Resistance N/mm 129
104.39 108.94 53.17 Tear Elmendorf, ISO6383-2 TD Relative Tear
Resistance N/mm 478.76 411.02 417.44 362.9
TABLE-US-00006 TABLE 5 Film testing after MDO Stretching 1:3 IE1
IE2 Dowlex 2045S FK1820A-02 MDO Stretch 1:3 Initial thickness .mu.m
25 25 25 25 4.4 m/s, 23.degree. C. Final thickness .mu.m ~12.5
~12.5 ~12.5 ~12.5 Stretch Ratio 1:3 1:3 1:3 1:3 Initial Width mm
600 600 600 600 Final Width mm 350 350 350 350 T .degree. C.
Stretching Roll .degree. C. 22 22 22 22 Puncture, ISO7765-2 Peak
Force N 36.1 35.3 22.1 26.1 Peak Force SD 1.1 2.7 1.8 3.1
Deformation @ Peak Force mm 22.3 33.1 20 17.8 Total Penetration
Energy J 0.6 0.8 0.3 0.3 Film thickness .mu.m 12 12 2 12 Normalised
Peak Force N/mm 3007.4 2942.6 1842.7 2175 Normalized Energy to Peak
Force J/mm 32.3 59.8 22 21 Normalized Total Penetration Energy J/mm
52.2 67.9 24.7 27 Tear Elmendorf, ISO6383-2 MD Relative Tear
Resistance N/mm 194.91 198.45 108.57 99.05 Tear Elmendorf,
ISO6383-2 TD Relative Tear Resistance N/mm 411.7 419.41 371.63
321.64
TABLE-US-00007 TABLE 6 Summary IE1 IE2 Dowlex 2045S FK1820A-02
Before stretching Normalised Peak Force N/mm 1505.7 1680.8 1322.7
1696.4 Normalized Energy to Peak Force J/mm 32 51 23.5 76
Normalized Total Penetration Energy J/mm 37.7 57 24.5 96.4 1:2
stretch Normalised Peak Force N/mm 2610 2615.9 1491.9 1633.5
Normalized Energy to Peak Force J/mm 82.6 93.8 18.8 22.1 Normalized
Total Penetration Energy J/mm 84.6 94.7 25.5 26 1:3 stretch
Normalised Peak Force N/mm 3007.4 2942.6 1842.7 2175 Normalized
Energy to Peak Force J/mm 32.3 59.8 22 21 Normalized Total
Penetration Energy J/mm 52.2 67.9 24.7 27 Materials show major
increases in peak force, and penetration energy.
TABLE-US-00008 TABLE 7 Data in full GPR GPR split Loop1 Loop1 split
Loop2 Loop2 GPR Powder Powder GPR Pellet Pellet P- ellet FRR Final
GPR Lot 1-2 Density MFR2 2-2 Density MFR2 Split Density MFR5 MFR21
Density MFR- 5 MFR21 21/5 MFR2 Density IE1 16.9 951.8 189 22.8
952.1 240 58.1 916.5 1.73 43 920 1.9 45.8 24.11 0.- 49415 896.9 IE2
16.7 951.9 206 23 953 348 58.1 916.4 0.61 21 917.2 2.3 57.2 24.87
0.59- 818 891.4
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